1. Field of the Invention:
This invention relates to an improvement in securing excellent quality in mutual radio communication paths between plural radio stations in a radio data communication system, and an effective investigation for finding out an optimum spot for locating a stationary radio station, such as a central data processing unit, in a facility wherein a plurality of portable radio terminals, such as handy bar-code readers, are provided.
2. Related Art:
Many of advanced factories have recently employed production lines whose production is totally administrated by using bar codes. More specifically, each area (i.e. a work or production station) in a factory is provided with a dedicated handy radio bar-code reader to read information from respective bar codes put on parts or components conveyed on the production line. The readout information are radio transmitted from respective handy bar-code readers to a central data processing unit for processing collected data as a whole. In this manner, usage of portable radio terminals in data transmission is widespread nowadays.
However, radio communications are generally inferior to cable communications in their communication qualities; thus the data transmissions using radio waves are inherently subjected to relatively higher error rates. For example, the presence of any obstructions in the communication path will worse the stability of electric field intensity in received radio waves, and the presence of disturbance radio noises will deteriorate the communication quality of radio transmission. Therefore, in introducing such a radio data communication system, it will be inevitably necessary to confirm the communication quality for assuring reliability and to find out an optimum spot for installing the stationary station.
According to conventional technologies, there is proposed an idea that electric field intensity information and noise information are used for judging the communication quality at a portable radio station (refer to the unexamined Japanese patent application No. 5-207844/1993). Or, there is known an idea that a test of radio communication quality is performed by measuring bit errors of a test signal between stationary and portable radio stations (refer to the unexamined Japanese patent application 62-224134/1987).
However, according to the technology disclosed in the unexamined Japanese patent application No. 5-207544/1993, the communication quality judged is unidirectional because the communication quality in this case only reflects the data measured in the data transmission from the opponent radio station to the concerned portable radio station. If any noise source exists in the vicinity of the portable radio station, this noise source will give an adverse effect to the evaluation of the communication quality between the stationary and portable radio stations. In other words, relying such a unidirectional measurement of communication quality is not accurate and not reliable in detecting the genuine quality of communication between the stationary and portable radio stations.
On the other hand, according to the technology disclosed in the unexamined Japanese patent application No. 62-224134/1987, the bit error measurement data reflects a unified or totalized quality in the radio communication between the stationary and portable radio stations. If radio signals emitted from the stationary radio station are different from those emitted from the portable radio station in their frequencies or output powers, the communication quality will be different in each communication path, i.e. in a data transmission path from the stationary radio station to the portable radio station, and in the other data transmission path from the portable radio station to the stationary radio station. Thus,.measuring a unified or totalized communication quality between the stationary and portable radio stations is not accurate and not reliable in detecting the genuine communication quality in each data transmission path between the stationary and portable radio stations.